diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 5b300cad230..ac701cf2633 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -443,6 +443,10 @@ Release 2.5.0 - UNRELEASED
     HDFS-6499. Use NativeIO#renameTo instead of File#renameTo in
     FileJournalManager. (Yongjun Zhang via atm)
 
+    HDFS-6518. TestCacheDirectives#testExceedsCapacity should
+    take FSN read lock when accessing pendingCached list.
+    (wang)
+
   OPTIMIZATIONS
 
     HDFS-6214. Webhdfs has poor throughput for files >2GB (daryn)
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestCacheDirectives.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestCacheDirectives.java
index 8ef3887dd56..bb8ef969168 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestCacheDirectives.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestCacheDirectives.java
@@ -1408,12 +1408,17 @@ public class TestCacheDirectives {
    */
   private void checkPendingCachedEmpty(MiniDFSCluster cluster)
       throws Exception {
-    final DatanodeManager datanodeManager =
-        cluster.getNamesystem().getBlockManager().getDatanodeManager();
-    for (DataNode dn : cluster.getDataNodes()) {
-      DatanodeDescriptor descriptor =
-          datanodeManager.getDatanode(dn.getDatanodeId());
-      Assert.assertTrue(descriptor.getPendingCached().isEmpty());
+    cluster.getNamesystem().readLock();
+    try {
+      final DatanodeManager datanodeManager =
+          cluster.getNamesystem().getBlockManager().getDatanodeManager();
+      for (DataNode dn : cluster.getDataNodes()) {
+        DatanodeDescriptor descriptor =
+            datanodeManager.getDatanode(dn.getDatanodeId());
+        Assert.assertTrue(descriptor.getPendingCached().isEmpty());
+      }
+    } finally {
+      cluster.getNamesystem().readUnlock();
     }
   }